This invention is directed to a film feed control device and control circuits thereof which are utilized to dispense film independent from other film moving mechanisms on a form, fill and seal packaging machine.
Many commodities are packaged on form, fill and seal packaging machines. Packaging pouches are formed on these machines from rolls of polymeric or metallized film or combinations of the same. The pouches are formed, filled and sealed and then disconnected from one another from an advancing stream of pouches on the machine.
To form, fill and seal the package several individual steps or stages are utilized on the machine. First front and back films, dispensed from film rolls, are sealed together along side seams utilizing side seal bars. Next a cross seam is formed between the side seams. Normally the cross seam serves both to form the top seam of a bottom most pouch and the bottom seam of the pouch immediately above it.
After the cross seam is made between the side seams the pouch can then be filled with a product. A further cross seam is made to form the top seal on the filled pouch and concurrently as noted above the bottom seal on the next descending pouch. The completely filled and sealed pouch is then severed from the ascending stream of pouches.
The individual hardware components needed by the above described pouch machines for forming, filling and sealing the pouches include side seal bars for forming the side seals, cross seal bars for forming the cross seal, a cut off knife for separating the individual pouches from one another and a fill tube and product reservoir connected thereto for adding product to the pouches as they are formed. Additionally, some means must be provided for advancing the film through the individual component apparatuses of the machine. This is typically done utilizing "pull" wheels or rollers.
Normally, sets of opposing pull wheels are displaced below the side seal bars. After the side seams are formed by the the side seal bars these pull wheels engage the film and advance it on the machine an increment amount corresponding to the dimension of a pouch being formed on the machine. The cross seals are then formed, product is added, the side seal bars again contact the film and the film is now ready to once again be advanced or indexed by the pull wheels.
For smooth trouble free operation and for the formation of consistent pouches on a form, fill and seal pouch packaging machine, it is important that the films be pulled the correct increment amount on the machine by the pull wheels and that the orientation of the film with respect to the individual components of the machine be properly maintained. Side to side movement or other misalignment of the film can result in improperly formed and thus unusable pouches.
The pull wheels or pull rollers in engaging the film to index or move the film on the pouch packaging machine rely upon friction between the wheels and the film. Normally the pull wheels are maintained at a constant speed of rotation and moved in and out toward and away from the film via appropriate mechanical or hydraulic mechanisms. The speed of the wheels is maintained constant and the length of film moved through the machine at each index or step is governed by the time of engagement of the pull wheels with the film.
Film for the above described form, fill and seal pouch packaging machine is available from various manufacturers on rolls. These rolls are loaded on arbors on the form, fill and seal packaging machine. The film is unwound from the rolls suspended on the arbors and then feed through the individual components of the machine.
Several interrelated factors govern how much force is necessary to unroll the film from the rolls of film. A new roll of film will have a large mass of film located thereon. To unroll the film sufficient force must be applied to the film to rotate the mass of the film about the arbor. Since the film is unrolling from the roll of film at a tangent to the circumference of the roll of film, the lever arm applied to the film to induce angular acceleration to unroll the film varies as the diameter of the roll of film changes from a large diameter for a full roll of film to a small diameter for a nearly empty roll of film. Thus as film is unrolled off the roll concurrently the mass of the roll of film decreases and so does the lever arm tending to unroll the film; however, these concurrent decreases may or may not be proportional.
Additionally, some films tends to adhere more tightly to themselves in a roll compared to other films. Also uneven force may have been applied in rolling the film in the first place creating a roll of film having one edge of the film more tightly bound and/or stretched compared to the opposite edge of the film.
All of these factors influence and continually change the force necessary to unwind a roll of film. In order to insure constant and perfectly formed pouches on the pouch packaging machine, an even tension should be kept on the roll of film at all times. In order to provide such an even tension, tension devices have been incorporated on form, fill and seal packaging machines. These tension devices attempt to apply an even tension to the film such that the film can be smoothly and consistently pulled by the pull rollers.
In one prior method of applying even tension to the film being unrolled from a roll, a "dancer bar" is utilized to maintain an even constant weight on the film and thus a constant tension on the film. For the dancer bar to work properly the film must be tense not only between the pull rollers and the dancer bar, but also between the dancer bar and the roll of film. This thus required the incorporation of mechanical linkages between the dancer bar and the film roll to allow unrolling of the roll of film only at such time as insufficient film is located between the dancer bar and the film roll and to inhibit unrolling of the film when sufficient film is located between the roll of film and the dancer bar. In one such device when excess film was present the dancer bar would descend tensing a leather strap against the arbor on which the film was loaded acting as a break against rolling of further film from the roll on the arbor. In such a system the size of the roll of film which could be located on the arbor was limited to an amount of film whose mass could be inhibited from rolling by the limited friction available by the weight of the dancer bar pulling on the leather strap.
Further, prior film feed systems had no provision for identifying when a roll of film was depleted. If an operator was not monitoring the machine when the roll of film was exhausted the machine would still operate; however, instead of incorporating product in pouches since there was no film and thus no pouches the product would be dispensed onto the machine components. Aside from wasting product this required clean up of the machine and possibly the work area prior to re-supplying the machine with new rolls of film and restart up of the operation.
Additionally, since start up of the machine requires operator attention to thread the film through the machine and insure that the side seals and cross seals are being properly formed prior to the start of product introduction, each time film must be loaded on the machine production must be halted. This naturally decreases the efficiency of operation.
In view of the above it is evident that these exists a need for new and improved film feed control devices for form, fill and seal packaging machines to insure (a) proper tension control of film being fed onto the packaging machine, (b) automatic sensing and shut down of the machine upon depletion of its supply of film and (c) longer run time intervals between re-supplying film.